The present invention relates generally to a device and method for protecting printed circuit board solder pads that are used to support integrated circuits (ICs) packaged using chip-on-tape (COT) techniques. More particularly, a pad cover is disclosed which is used to protect the solder pad to which a chip-on-tape packaged IC will be attached before or after wave soldering operations.
During the assembly of computer boards such as motherboards, it is common to mount numerous components on a first surface of a printed circuit board (PCB). Often, many of the components include pins that extend through holes in the printed circuit board and are soldered thereto at the back surface of the PCB. At the same time, a number of surface mounted devices including capacitors, resistors, inductors and certain surface mounted integrated circuits may also be mounted on the back surface of the PCB. One cost effective approach to securing both the pins of the through mounted components mounted on the top surface and the pins/leads of the surface mounted components mounted on the bottom surface is known as a wave solder. During a wave solder operation, an assembled board is run through an oven over a molten solder fountain. The molten solder is exposed to the back surface of the board. The solder attaches to metallic components and solidifies to bond both the through mounted components from the top surface and the surface mounted components from the bottom surface to the printed circuit board.
In the ongoing efforts to provide increased computational power in smaller units, convention plastic encapsulation packaging of integrated circuits has sometimes given way to chip on tape (COT) packaging. Chip on tape packaging is also sometimes referred to as tab automated bonding (TAB). COT packaging has several superior electrical characteristics when compared to conventional plastic encapsulation packaging. Most notably, COT packaging has lower inductance, lower capacitance and no internal ground plane. Furthermore, COT packages are smaller, which provides shorter trace lengths, decreasing the inductance and COT packages can have more pins which allow for more ground pins which in turn allows the use of more powerful drivers. Since COT packages are much smaller than conventional packaging techniques and have the described advantages, there are some good incentives to utilizing such packaging in boards used in computer systems.
When a high powered integrated circuit (IC) is packaged in COT, there may be a need to provide a heat sink which helps dissipate excess heat generated by the IC. Applicants have found that a convenient way to couple a heat sink to a COT packaged IC is to mount the COT packaged IC on the bottom surface of the computer board while mounting a heat sink on the top surface directly opposite the COT packaged IC. A number of thermal vias are provided through the motherboard PCB between the COT packaged IC and the heat sink to insure that good cooling is obtained using an inexpensive, relatively uncomplicated structure. One reason to mount the IC on the bottom surface of the computer board (rather than the top) is that the heat sink typically has a relatively high profile and most computer mother boards have a relative low clearance on the bottom surface. One drawback of this design, however, is that having exposed COT packaged ICs or exposed COT solder pads on the bottom surface of the computer board would preclude the wave soldering operation described above.
Accordingly, it is an object of the present invention to provide a pad cover suitable for protecting solder pads for COT packaged ICs that are exposed to a wave soldering operation.